Crash-based safety analysis is set back by several shortcomings such as randomness and rarity of crash occurrences, lack of timeliness, and inconsistency in crash reporting. Non-crash-based safety analysis has been around for more than three decades but its potential was limited due to a difficulty in the data collection and the evaluation. Recent advancement in digital videos and image detection technology renewed our interest in facilitating the data collection and improving the evaluation method. Two image detection systems for the measurement of traffic characteristics were evaluated: (a) a commercial video detection system and (b) proprietary image processing software. The measurement evaluation revealed that both systems were still not sufficiently accurate for the safety evaluation purpose and thus a manual measurement from digitized video clips was preferred for a collection of evaluation data. We proposed a novel application of extreme value theory to safety evaluation based on observable traffic characteristics. The proposed method was evaluated by applying to right-angle collisions at signalized intersections. A traffic characteristic so-called post-encroachment time (PET) was collected at selected intersections as a surrogate safety measure. Based on PET characteristics, risk and frequency of rightangle crashes at the studied intersection or individual conflict zone can be estimated using only the data collected at the location. For comparison, a traditional approach to safety analysis using Poisson and negative binomial regression analyses was also examined. Both evaluation methods – extreme value approach and regression – indicate a significant relationship between PETs and historical crash data. Simulation experiments were carried out to examine the effect of observation period on a variance of estimates obtained the proposed method. Advantages and problems with the proposed method are described in this study. A simple method for an evaluation of the risk of right-angle collisions at signalized intersections is also provided in the appendix.

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safety evaluation, extreme value theory, risk estimation, surrogate safety measure, right-angle collision, video image processing, post-encroachment time, SPR-2663

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Performing Organization

Joint Transportation Research Program

Publisher Place

West Lafayette, IN

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